A whole kilometre of underground telephone cable was stolen from a country road near Lewes.
The cable, which is expected to cost £45,000 to replace, was taken from the B2108 between the roundabout for Drusillas Zoo Park and Alfriston.
Workers discovered the cable - which served 800 home or business telephones, had been cut at 4am on Wednesday.
The crime is believed to have taken place between 1am and 2am.
A spokeswoman for Sussex Police said: "It is believed a vehicle may have been used to pull it out of the ground and then the same or a waiting vehicle used to transport it."
PC Thomas Stallard said: "Police are seeking any witnesses who may have seen anyone prior to this time or during the hours stated, even if they looked to be official work people on the site."
Anyone with information is asked to call Sussex Police on 0845 6070999, quoting serial 204 of October 28.